Certain products, such as baby food, are packaged under a partial vacuum in containers having a domed metal cap. These domed caps are concave when a proper vacuum is maintained in the container. If the vacuum is lost, the domed portion pops up to provide a visual indication of an improperly sealed container, commonly called a dud.
Because of the critical need for insuring that baby food containers are properly sealed, various types of nondestructive dud detecting apparatus have been developed. One type is positioned above a conveyor along which boxes of sealed containers pass. These dud detectors are used to sense the presence of the proper vacuum or pressure within the container in a variety of manners. See, for example, U.S. Pat. Nos. 3,802,252; 3,832,885; 4,213,329 and 4,117,718, all assigned Benthos Incorporated of North Falmouth, Mass. Since many of the currently available dud detectors can be used even though the containers are packaged in sealed cardboard boxes, testing can be conducted at any time, even immediately prior to shipping.
One way to conduct nondestructive testing of 100% of the containers is to have boxes of the containers fed along a conveyor. With this testing technique a number of dud detectors are positioned above the conveyor at positions directly overlying the containers within the passing boxes. Typically, a box of baby food jars will have four rows of jars packed adjacent one another; four dud detectors are arranged above the conveyor equally spaced from one another to directly overlie the rows of jars in the boxes as they pass underneath the detectors.
Although this system permits the inspection of all containers, containers having different diameters require that the dud detectors be repositioned to achieve the appropriate spacing. Repositioning using conventional mounting apparatus is a cumbersome and time-consuming process thus reducing flexibility in the use of the dud detector inspection equipment.